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Visual Signals of The East Pacific Red Octopus (Octopus rubescens) During Conspecific Interactions

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Abstract and Figures

Multiple species of octopuses have recently demonstrated the use of specific visual signals (such as chromatic, postural, locomotor, and textural indicators) to communicate with conspecifics. This study aimed to identify the visual signals of the East Pacific red octopus, Octopus rubescens, during interactions with conspecifics. Octopus rubescens were collected from Admiralty Bay, WA – a habitat littered with discarded glass bottles which O. rubescens opportunistically use as dens. To identify the visual signals of O. rubescens, GoPro cameras recorded videos of octopuses interacting with conspecifics of the same and opposite sex in an observation tank over the course of 15 min. Octopus rubescens were predominantly aggressive toward conspecifics, but nonetheless displayed visual signals, such as ‘upright’, ‘attack’, ‘approach’, ‘ochre’, and ‘dark ochre’, which were recorded in an ethogram. Due to the unique, bottle-dense habitat of Admiralty Bay, the observed visual signals of O. rubescens may be specialized compared to other O. rubescens individuals living in different, but more natural habitats. Consequently, the ethogram produced in this study may be used as a source of comparison for future studies documenting the visual signals of this species in other habitats; this could reveal potential variations in visual signals and may suggest that the visual signals used by O. rubescens are influenced by their surroundings.
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Diving For Science 2019
Proceedings of the
American Academy of Underwater Sciences
38th Scientific Symposium
Co-hosted by
Canadian Association for Underwater Science
Isabelle M. Côté and E. Alan Verde
Co-Editors
Simon Fraser University
and Vancouver Aquarium
Vancouver, British Columbia, Canada
October 8 – 11, 2019
Diving For Science
2019
Proceedings of
the
American Academy of Underwater
Sciences
38th Scientific
Symposium
Co-hosted by
Canadian Association for
Underwater Science
Isabelle M. Côté and E. Alan Verde
Co-Editors
Simon Fraser University and Vancouver Aquarium
Vancouver, British Columbia, Canada
October 8
11,
2019
ii
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Côté, I.M. & Verde, E.A., eds. Diving for Science 2019:
Proceedings of the American Academy of Underwater Sciences 38th Symposium.
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Visual Signals of The East Pacific Red Octopus (Octopus rubescens)
During Conspecific Interactions
Rachel L. Borisko1, Kirt L. Onthank2, E. Alan Verde1,*
1 Maine Maritime Academy, 1 Pleasant Street, Castine, ME 04420, USA
2 Walla Walla University, 204 South College Avenue, College Place, WA 99324, USA
*alan.verde@mma.edu
presenting and * corresponding author
Abstract
Multiple species of octopuses have recently demonstrated the use of specific visual signals (such as
chromatic, postural, locomotor, and textural indicators) to communicate with conspecifics. This study
aimed to identify the visual signals of the East Pacific red octopus, Octopus rubescens, during
interactions with conspecifics. Octopus rubescens were collected from Admiralty Bay, WA a habitat
littered with discarded glass bottles which O. rubescens opportunistically use as dens. To identify the
visual signals of O. rubescens, GoPro cameras recorded videos of octopuses interacting with
conspecifics of the same and opposite sex in an observation tank over the course of 15 min. Octopus
rubescens were predominantly aggressive toward conspecifics, but nonetheless displayed visual signals,
such as ‘upright’, ‘attack’, ‘approach’, ‘ochre’, and ‘dark ochre’, which were recorded in an ethogram.
Due to the unique, bottle-dense habitat of Admiralty Bay, the observed visual signals of O. rubescens
may be specialized compared to other O. rubescens individuals living in different, but more natural
habitats. Consequently, the ethogram produced in this study may be used as a source of comparison for
future studies documenting the visual signals of this species in other habitats; this could reveal potential
variations in visual signals and may suggest that the visual signals used by O. rubescens are influenced
by their surroundings.
Keywords: cephalopods, communication, conspecifics, Octopus rubescens, visual signals
Introduction
Historically, octopuses have been thought to be solitary, asocial individuals (Barbato et al., 2007;
Hanlon and Messenger, 2018); however recent studies have suggested that octopuses use a unique and
systematic arrangement of visual signals to communicate with conspecifics (Huffard, 2007; Caldwell
et al., 2015; Scheel et al., 2016). These visual signals include chromatic and textural changes, postures,
different forms of locomotion, and inking, which can be combined or used consecutively to create
specific displays (Hanlon and Messenger, 2018). Displays are characterized by being repetitive and
discrete, allowing octopuses to portray clear messages to receivers.
Some of the most complex signals octopuses use are chromatic signals. Since octopuses have direct
neural control of pigment-containing cells, called chromatophores, octopuses can quickly change
chromatic signals, adjust signal strength, and even perform bilateral signaling (Barbato et al., 2007;
Hanlon and Messenger, 2018). Hanlon and Messenger (2018) have observed that chromatic signals
generally include forming line-stimuli consisting of bands (lines, stripes, bars) or spots that are easily
detected by other octopuses. Although colorblind, octopuses have excellent vision consequently, by
using highly contrasting chromatic signals, octopuses can clearly display their intent (e.g. to show
dominance or submissiveness) toward a conspecific (Tricarico et al., 2011; Hanlon and Messenger,
2018).
Côté, I.M. & Verde, E.A., eds. Diving for Science 2019:
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In combination with chromatic signals, textural signals (defined as smooth or papillate skin) can be used
to modify the appearance of an octopus. Additionally, postural signals, such as raised arms or flattening
of an octopus’s body, are often used to adjust an individual’s apparent size to demonstrate intimidation
or submissiveness (Hanlon and Messenger, 2018). Furthermore, specific movements, labelled
‘locomotor’ visual signals, may include chasing or fleeing (Hanlon and Messenger, 2018). All of these
signals can be combined in a wide variety of patterns and intensities, allowing octopuses to effectively
communicate with conspecifics.
Three species of octopuses that have been shown to use visual signals to communicate with conspecifics
include the larger Pacific striped octopus (Octopus sp.), the Algae octopus (Abdopus aculeatus), and
the common Sydney octopus (Octopus tetricus) (Huffard, 2007; Caldwell et al., 2015; Scheel et al.,
2016). Each of the studies described specific visual signals used by octopuses during conspecific
interactions that were typically agonistic. Both Huffard (2007) and Caldwell et al. (2015) performed
observational studies and recorded octopuses’ visual signals in ethograms which act as libraries that
describe and identify behaviors displayed by animals.
Many visual signals that octopuses utilize are species-specific, therefore characterizing and
documenting visual signals of octopuses via ethograms provides useful supplementary information for
validating species identification (Barbato et al., 2007; Huffard, 2007). Additionally, both Sinn et al.
(2001) and Scheel et al. (2016) suggest that ethograms can act as resources for scientists studying how
ecological influences, such as conspecific interactions or habitat availability, may affect the evolution
of signal development or communication. For example, a population of octopuses living in one type of
habitat may utilize a slightly different or more specialized set of visual signals to communicate with
each other compared to a population of the same species living in a different type of habitat.
Although 19 common visual signals were identified for the East Pacific red octopus (Octopus
rubescens) by Mather and Anderson (1993), these signals were in response to human stimuli during
three different situational laboratory tests. No ethogram has been created to describe the visual signals
used by O. rubescens while interacting with conspecifics. Octopus rubescens is a subtidal species found
along the west coast of North America (from Alaska to California), sheltering in kelp beds and rocky
areas, and are commonly found in Admiralty Bay, WA (Cowles, 2005). The benthic habitat of this bay
is generally barren and flat, characterized by mud, sand, and small rocks, with few hiding places for this
non-burrowing octopus species. However, the bay is littered with discarded glass bottles which O.
rubescens opportunistically use as dens (Anderson et al., 1999). Octopus rubescens have capitalized on
this new habitat source which may have inadvertently concentrated individuals of this species within
the bay (Chase and Verde, 2011). Consequently, O. rubescens may interact with conspecifics more
frequently within this “artificial” environment and these interactions may be characterized by visual
signals used by octopuses to communicate with each other.
Given that octopuses use visual signals to interact, the purpose of this project was to determine the
frequency of such signals used by O. rubescens individuals to communicate with conspecifics, and to
document those visual signals in an ethogram. As such, this study addressed the following questions:
1) What are the visual signals that O. rubescens use during interactions with conspecifics?
2) Is the frequency of interactions influenced by the sex of octopuses?
3) Do the type or frequency of visual signals differ between initiators and reactors of an interaction?
Côté, I.M. & Verde, E.A., eds. Diving for Science 2019:
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Methods
Overview
To identify the visual communication signals of O. rubescens, cameras recorded videos of octopuses
interacting with conspecifics of same and opposite sex in an observation tank. Videos were analyzed
for any visual signals used by the octopuses during interactions and these visual signals were defined
and categorized in order to assemble an ethogram for O. rubescens.
Octopus collection and care
Octopus rubescens individuals were collected via SCUBA from Admiralty Bay, WA (48°9’43.84” N,
122°38’4.67” W) and housed at the Rosario Beach Marine Laboratory (RBML), Anacortes, WA.
Because this species is often found inhabiting bottles in this bay, all bottles found were checked for the
presence of O. rubescens by scraping away any biofouling on the bottle. If an octopus without any eggs
was present, the bottle was collected and placed into a Ziploc® (3.8 L) bag and sealed. Upon completion
of each dive, collected octopuses were removed from their resident bottles and transferred to red
Nalgene© (1 L) bottles. The Nalgene© bottle openings were covered with plastic window screen mesh
and secured to the bottle by an elastic rubber band. Bottles were placed in a cooler containing aerated
seawater and transported back to RBML; all ‘home’ glass bottles, or dens, were returned to the ocean
prior to leaving the collection site.
Upon arrival to RBML, all octopuses were weighed (g) and their sex determined. Weight was measured
by placing a tared jar partially filled with seawater onto a Mettler ToledoTM balance (Model: PL601-S).
Individual octopuses were persuaded into the tared jar from their Nalgene© bottle by emptying all
seawater from the Nalgene© bottle and holding it above the jar on the scale until octopuses transferred
themselves. Octopus mass ranged from 18.8 - 68.0 g, with the average mass being 42.0 g. Octopus sex
was determined by looking for the presence of a hectocotylus, the third right arm on male octopuses
modified to carry spermatophores; this arm is enlarged and lacks suckers at its tip (Cowles, 2005). Mass,
sex, date collected, and the octopus’s location in the lab were recorded in a Google spreadsheet.
Individual octopuses were housed in enclosed, opaque plastic containers (36 cm x 23 cm x 28 cm; Chase
and Verde, 2011) with constant flowing ambient seawater via a manifold system (Figure 1). Rocks were
placed on top of the containers as additional measures to prevent octopuses from escaping. The enclosed
containers were held in seawater raceways (231 cm x 29 cm x 24 cm) to maintain a constant temperature
of 12 °C (Perron and Verde, 2015). Octopus rubescens have been noted to adapt well to captivity and
most octopuses are known for being exploratory and responsive to laboratory conditions (Mather,
2006). Each octopus was given a minimum of 48 h to acclimate to the containers and sea water system
and were fed purple shore crabs (Hemigrapsus nudus). Octopuses were fed once per day at night, after
all tests were concluded for the day, to avoid the potential influence of increased metabolism (due to
specific dynamic action) on social behaviors (Katsanevakis et al., 2005; Hill et al., 2016).
The total sample size (N) for this experiment was 20 octopuses (10 males & 10 females). The seawater
system at RBML dedicated for this study could house a maximum of 10 octopuses at a time, so the
study was divided into halves. One set of 10 octopuses was run through all tests while the second set of
10 octopuses was collected. Upon completing all tests, octopuses were released back into Admiralty
Bay; release locations were separate from new octopus collection sites within the bay to prevent
recollection. Sets of octopuses were assigned letters, to identify the respective sets that octopuses were
from (A = set 1, B = set 2). Each set of octopuses participated in the Conspecifics treatments’ (see
below). The sex ratio for this study was 50/50 female to male octopuses, to represent the typical sex
ratio found in the local area for this species (Chase and Verde, 2011). Octopuses were identified by
their respective locations in the seawater table (e.g. a female octopus in seawater table “H” in container
“2” was identified as “H2”).
Côté, I.M. & Verde, E.A., eds. Diving for Science 2019:
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Figure 1. Holding tanks for the maintenance of Octopus rubescens. Individual octopuses were housed in
enclosed, opaque plastic containers with constant flowing ambient seawater via a manifold
system. Containers were maintained in seawater raceways to maintain a constant temperature
of 12 °C.
Observation tank
A flow-through seawater observation tank (80 cm x 50 cm x 24 cm) was outfitted with three GoPro
cameras (Figure 2) and placed in a closed room to avoid unnecessary humanoctopus interaction while
tests were conducted. The tank was divided by a piece of plexiglass with holes drilled into it to buffer
the rippling effect of the seawater in/outflow (Figure 2). Consequently, only half of the tank (46 cm x
50 cm x 24 cm) was used as the testing area for the octopuses. Overhead fluorescent lights provided
illumination for the cameras and octopuses were given a minimum of 48 h to acclimate to the laboratory
lighting conditions. This highly illuminated environment was necessary to capture clear videos of the
octopuses and camera settings were adjusted (see Appendix) to accommodate for the lighting. These
settings ensured that the highest-quality videos were recorded. To reduce glare for the overhead camera,
some fluorescent light bulbs were removed and white sheets were hung under the lights to filter the
light above the tank. The observation tank was white, which provided sufficient contrast between the
octopuses and the tank for the cameras to successfully record images. To improve water clarity, two
seawater filters were attached to the seawater input lines of the tank. Cotton balls were used as the
filtering material in the seawater filters and were changed as needed, typically every two to three days.
The observation tank was cleaned, drained, and refilled every morning before any tests commenced.
Cameras were placed at different locations in the tank (Figure 2), one directly above and two submerged
at the octopuses’ level in opposite corners of the tank. Plexiglass stands (Figure 3A) were made to hold
the cameras in place (Figure 3B). To eliminate blind spots for the corner cameras in the tank, two
plexiglass dividers were cut and angled width-wise along the tank walls to narrow the space (Figure 2).
GoPro cameras were left on and recording independently for the duration of each 15-min trial and
videos were downloaded to a personal computer after each trial. The tank was drained and completely
flushed at the end of every trial to ensure chemicals released by octopuses (e.g. ink, pheromones,
nitrogenous waste) during interactions did not influence subsequent trials.
Côté, I.M. & Verde, E.A., eds. Diving for Science 2019:
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Figure 2. Experimental set-up for the study of visual signals used by Octopus rubescens. A flow-through
seawater observation tank was outfitted with three GoPro cameras (red circles). The tank was
divided by a piece of plexiglass (larger, yellow rectangle) with holes drilled in it to buffer the
rippling effect of the seawater in/outflow (green oval). Only half of the tank was used as the
testing area for the octopuses. To eliminate blind spots for the corner cameras in the tank, two
plexiglass dividers were cut and angled width-wise along the tank walls to narrow the space
(smaller, orange rectangles).
Figure 3. Fabricated plexiglass frames (A) that secured cameras to the corners of observation tank (B).
A.
B.
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Since O. rubescens have been noted to display aggressiveness toward conspecifics (Mather and
Anderson, 1993; Scheel et al., 2016), octopuses were separated in the observation tank space with a
piece of plexiglass as a precautionary step while conducting preliminary trials (see ‘Ethogram section
below). Most octopuses were aggressive toward one another, but not cannibalistic or noticeably
harmful, therefore the plexiglass divider was not used for all other trials following the preliminary trials.
Ethogram
To observe and gather baseline visual communication signs displayed by O. rubescens, multiple trial
runs of the Conspecifics treatment (see below) were made with octopuses previously caught and
already at RBML. These visual signals observed were compiled into a basic ethogram and used to
categorize additional signs observed during the rest of the study. Visual signals (Table 1) were described
utilizing the terminology compiled by Hanlon and Messenger (2018). Ethogram terminology was also
adapted from Huffard (2007), Caldwell et al. (2015), and Scheel et al. (2016). These signs included:
chromatic (e.g. banding, spots, darkening) and papillae change (e.g. papillate or smooth), forms of
locomotion (e.g. chasing, fleeing), and postures (e.g. spreading or flattening of body, raised arms). As
additional visual signals were observed, they were added to the basic ethogram library to create the final
ethogram for this species.
Table 1. Visual signals cephalopods may utilize during conspecific interactions. These terms were used
to describe recorded visual signals of interacting O. rubescens conspecifics in an observation
tank. Adapted from Hanlon and Messenger (2018).
Chromatic
Signals
Textural
Signals
Locomotor
Signals
Postural
Signals
Inking
Signals
Whole body
Papillate
Chase
Whole body
Pseudomorphs
General paling
Smooth
Flee
Orientation to receiver
Intense whitening
Forward rush
Up/downward pointing
General darkening
(Anti)parallel
position
Spreading
Flashing (pulsating)
Flattening
Passing cloud
Conflict mottle
Arms only
Singly
Partial (often unilateral)
In pairs or all together
False eyespots
Raised or lowered
Dark arms
Splayed
Dark spots (large or
small)
Split
Suckers (white or dark-
edged)
V-curled
Dark eye rings
Contorted
Dilated pupil
Male ligula
presentation
Dark stripes or streaks
(longitudinal)
Dark bars, bands or rings
(transverse)
Bright white spots (large
or small)
Zebra bands or flame
markings
Lateral mantle blush
Fin lines (dark or light)
Accentuated white gonad
Red nidamental glands
Iridescent rings or stripes
Polarized light from arms
Côté, I.M. & Verde, E.A., eds. Diving for Science 2019:
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Conspecifics treatment
Each octopus (in a set of 10 octopuses) was allowed to interact with all other octopuses of the same and
opposite sex within each set (Figure 4). Treatments were as follows: male and male (M/M), male and
female (M/F), and female and female (F/F). The order of the octopus combinations was chosen via
simple random sampling and random numbers were assigned to each possible octopus combination. To
ensure no octopus individual was tested consecutively, selected numbers could be ignored and re-
entered into the random numbers table. Tests were performed each day (Sunday to Friday) until all
octopus combinations were completed.
Figure 4. Interaction treatments used in study of visual signals by Octopus rubescens. Each octopus (in
a set of 10 octopuses) was allowed to interact with all other octopuses of the same and
opposite sex within each set (Male/Male, Male/Female, and Female/Female). Octopuses were
observed via GoPro cameras (red boxes) in an observation tank. The tank was divided by a
piece of plexiglass (black rectangle in tank) to buffer the rippling effect of the seawater
in/outflow (green hose, gray pipe).
Two octopuses were placed in the observation tank as far away from each other as possible. Octopuses
were placed in the tank one at a time, therefore the first octopus to enter the tank was always the octopus
that was listed first in the written combination name (e.g. combination “H3 and H7”; H3 would be
placed in the tank first). Once recording commenced, the octopuses were left to interact for 15 min, as
interactions were likely to occur within the first 15 min. Since these organisms are exploratory
(Onthank, pers. obs.), this interaction time was chosen to avoid leaving the octopuses in the observation
tank for an extended period of time. Octopuses were observed from a distance of at least 2 m to keep
track of individuals with no unique identifying characteristics (e.g. unique scars, missing arms) and to
intervene if necessary when interactions became too aggressive.
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Collecting and analyzing data
VLC Media Player was utilized to observe videos recorded by the GoPro cameras. Snapshots from the
videos were added to the basic ethogram created at the beginning of this project and subsequent videos
were analyzed using the basic ethogram. The ethogram was used to describe any octopus interaction
that lasted at least 5 s and any new visual signal observed during video analysis was added to the basic
ethogram. The approach of one octopus toward the other marked the beginning of an interaction with
the approaching octopus deemed the ‘Initiator’ and the other octopus the ‘Reactor’, as defined by Scheel
et al. (2016). When an interaction began, the time was noted and the visual signals (chromatic, textural,
postural, locomotor, inking) of the octopuses were recorded. When there was any change in a given
signal during an interaction, the new signal was recorded and the time was noted. A new interaction
was recorded only if there was more than a 5 s interval since the end of the last interaction (Sinn et al.,
2001). The total number and types of recorded signals displayed by the octopuses in the observation
tank were compiled into clustered bar graphs which showed proportions of signals observed within
certain categories (e.g. signal or sex categories); this demonstrated how frequently each of the signals
was used by octopuses. Due to some behavioral interactions having small sample sizes, comparative
statistical analysis could not be performed.
Results
Octopus rubescens used a variety of visual signals to communicate and interact with conspecifics during
the 15-min trials. These visual signs included chromatic (Figures 5 & 6), textural (Figure 7), inking
(Figure 8), locomotor (Figure 9), and postural cues (Figure 10). Additionally, signal names and
descriptions from the final ethogram were summarized and compiled (Table 2). The frequency of
interactions differed by 1 interaction per test between the M/M octopus combinations (5.2 interactions
per test) and M/F and F/F octopus combinations (4.2 interactions per test).
Figure 5. Partial-body chromatic signals used by O. rubescens. A.-B. False frontal white eye spots: two
adjacent white spots centered below eyes; C.-D. Dark longitudinal stripe(s): typically run(s)
from eye down first left and/or right arm(s); does not always run length of arm; E.-F.
Darkened arms: typically first left or right (or both) arms of octopus; all arms can be darkened;
G. Dark eye rings: darkened patch encircling eyes.
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Figure 6. Full-body chromatic signals used by O. rubescens. A. Pale: body is light ochre to gray or
white; B.-C. Mottled ochre: ochre/sandy-colored body; white and/or brown/black spots (spot
density and color varies) across entire body; D. Dark ochre: completely darkened body, red
to brown/dark ochre; E.-F. Deimatic: dark spots/patches on mantle, pale arms; G. Ochre:
ochre/sand-colored body (some variation in darkness); H.-J. Intense mottle: high contrast
between dark and pale markings on body, bars/bands of dark along arms may be present;
often papillate.
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Figure 7. Textural signals used by O. rubescens. A.-B. Smooth: no papillae; C.-D. Papillate: papillae
visibly raised.
Figure 8. Inking signal used by O. rubescens. Inking was recorded as either present or absent.
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Figure 9. Locomotor signals used by O. rubescens. A. Attack: octopus launches self at conspecific;
forward rush; jet propulsion commonly utilized; B.-C. Grappling: octopuses entangled in each
other’s arms, reaching, biting, grabbing. Signals not visualized: Stationary, Threaten, Flee,
Chase, Approach.
Octopus interactions (Figure 11) were typically characterized by the locomotor signals ‘stationary’
(45.9%), ‘approach’ (21.7%), and ‘flee’ (24.6%) by one or both octopuses for all sex combinations
(M/M, M/F, F/F). The most common chromatic signals included ‘ochre’ (44.3%), ‘dark ochre’ (21.9%),
and ‘pale’ (16.4%); octopuses appeared to primarily use ‘ochre’ as a resting pattern of pigmentation.
The most common postures included ‘upright’ (33.6%) and ‘curled arms’ (23.9%). Textural signals
were predominantly ‘smooth’ (77.2%) and octopuses rarely inked.
When interactions between octopuses were divided between the initiator and reactor within each sex
combination (M/M, M/F, F/F), locomotor signals (Figure 12) used by initiators of an interaction were
mostly characterized by ‘approach’ (36.6%), ‘flee’ (22.6%) or ‘stationary’ (32.8%), while reactors
predominantly expressed the signals ‘stationary’ (58.8%) or ‘flee’ (26.6%). Regarding chromatic
signals (Figure 13), initiators and reactors were most often ‘ochre’ (43.2% & 44.6%, respectively) or
‘dark’ (23.4% & 21.7%, respectively). The postural signals of both initiators and reactors (Figure 14)
were characterized by ‘upright’ (30.0% & 27.0%, respectively) and/or ‘curled arms’ (15.5% & 31.7%,
respectively) and many interactions were characterized by ‘reaching’ (12.1%) from initiators (Figure
14). The M/M paired octopuses grappled the most out of the three sex combinations (Figure 12 & 14);
however, grappling made up only 5.4% and 3.9% of locomotor and postural signals, respectively
(Figure 11).
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Figure 10. Postural signals used by O. rubescens. A. Spreading arms: arms stretched out; B. Flattened:
low to bottom, mantle lowered; C. Beak-to-beak: octopuses facing each other, touching
close to beaks; D. Reaching: one/multiple arms reaching for conspecific; E. Upright: alert
toward conspecific; F. Jetting: arms together, typically, but can be curled; G: Loose arms:
arms hanging loosely around/below body, can be slightly curled; H. Stand tall: upright, arms
straightened to make self taller/larger; I. Grappling: octopuses fighting; J. Attack: arms
poised to attack conspecific (two front arms typically curled and held up); often combined
with chromatic signal ‘Darkened arms’; K. Raised arms: arms raised, often curled; typically
front arms; L. Crawling: arms out, loose or curled, propelling octopus; M. Curled arms: arms
curled tightly against body.
Côté, I.M. & Verde, E.A., eds. Diving for Science 2019:
Proceedings of the American Academy of Underwater Sciences 38th Symposium.
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Table 2. Summary of visual signals (chromatic, textural, postural, and locomotor signals and inking)
used by O. rubescens during conspecific interactions observed during 15-min trials in an
observation tank. Terminology adapted from Huffard (2007), Caldwell et al. (2015), Scheel
et al. (2016), and Hanlon and Messenger (2018).
Visual Signals
Chromatic
Description
Pale
Pale body light ochre to gray or white.
Deimatic
Dark spots/patches on mantle, pale arms.
Ochre
Ochre/sand-colored body (some variation in darkness).
Mottled ochre
Ochre/sandy-colored body; white and/or brown/black spots (spot density and color varies)
across entire body.
Intense mottle
High contrast between dark and pale markings on body, bars/bands of dark along arms may be
present; often papillate.
Dark
Completely darkened body, red to brown/dark ochre.
Chromatic:
Partial Body
(Arms/eyes/mantle)
False frontal white eye
spots
Two adjacent white spots centered below eyes, on front part of octopus body.
Dark longitudinal
stripe(s)
Typically run(s) from eye down first left and/or right arm(s), can be symmetrical on other side
of octopus; does not always run length of arm.
Dark eye rings
Darkened patch encircling eyes.
Darkened arms
Typically first left or right (or both) arms of octopus. All arms can be darkened.
Textural
Smooth
No papillae.
Papillate
Papillae visibly raised.
Postural
Spreading arms
Arms stretched out, feeling bottom.
Flattened
Octopus low to bottom, mantle lowered.
Beak-to-beak
Octopuses facing each other, arms spreading around each other. Touching close to beaks.
Reaching
One or multiple arms reaching for conspecific.
Curled arms
Arms curled tightly against body.
Loose arms
Arms hanging loosely around or below body, can be slightly curled.
Upright
Octopus alert toward conspecific.
Jetting
Arms together, typically, but can be curled.
Grappling
Octopuses entangled in each other’s arms, fighting.
Stand tall
Upright, arms straightened to make self taller/larger.
Crawling
Arms out, loose or curled, but clearly being used to propel the octopus.
Attack
Arms poised to attack conspecific (two front arms typically curled and raised).
Raised arm(s)
Arms raised, often curled. Typically first front arms (left and/or right).
Locomotor
Stationary
Octopus not moving.
Threaten
Octopus lunges at conspecific but does not attack.
Flee
Octopus moves away from conspecific via crawling or jetting.
Attack
Octopus launches self at conspecific, forward rush. Typically jet propulsion.
Grappling
Octopuses entangled in each other’s arms, reaching/biting/grabbing.
Chase
Octopus pursues conspecific via crawling or jetting.
Approach
Inking
Present/Absent
Octopus approaches conspecific via crawling or jetting.
Ink.
Côté, I.M. & Verde, E.A., eds. Diving for Science 2019:
Proceedings of the American Academy of Underwater Sciences 38th Symposium.
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Figure 11. The percent occurrence of the most common visual signals displayed by O. rubescens during
interactions with conspecifics in an observation tank (Nmale = Nfemale = 10). The five
categories of signals include textural, locomotor, postural, inking, and chromatic which all
have a variety of subcategories.
Discussion
A variety of visual signals used by O. rubescens during conspecific interactions were identified and
catalogued in an ethogram. The number of interactions per test for all sex combinations (M/M, M/F,
F/F) of octopus was similar, which suggests that sex had little influence on the frequency of interactions
between octopuses. Both initiators and reactors typically used the same set of visual signals during
interactions; however, the sequence in which these visual signals were used was not analyzed.
Consequently, it cannot be concluded that a certain visual signal was correlated with initiating or ending
an interaction. While O. rubescens may gather in an area for a specific habitat resource, such as the
bottles used as dens in Admiralty Bay, the species demonstrated predominantly aggressive behavior
toward conspecifics during this study, suggesting that they are not a social species even if they are not
solitary. When interactions did occur, they were characterized by an approach, which was either
aggressive or exploratory (which often led to aggression), and ended with one or both octopuses
attempting to escape. Alternatively, octopuses would simply avoid each other, which can be interpreted
as another indication that this species is asocial. Nonetheless, O. rubescens still demonstrated the
utilization of multiple visual signals during interactions which suggests communication was occurring
between individuals.
0
10
20
30
40
50
60
70
80
90
100
Smooth
Papillate
Not Determined
Approach
Attack
Chase
Flee
Grapple
Stationary
Threaten
Spreading arms
Upright
Stand Tall
Reaching
Attack
Curled Arms
Loose Arms
Grappling
Raised Arms
Flattened
Beak-to-Beak
Present
Absent
Pale
Ochre
Dark Ochre
Mottled Ochre
Intense Mottle
Diematic
Textural Locomotor Postural Inking Chromatic
Percent Occurrence (%)
Visual Signals Observed
Côté, I.M. & Verde, E.A., eds. Diving for Science 2019:
Proceedings of the American Academy of Underwater Sciences 38th Symposium.
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Figure 12. Locomotor signals commonly used by initiators (A) and reactors (B) of an interaction.
Octopus rubescens were allowed to interact with conspecifics in Male/Male, Male/Female,
and Female/Female pairs in an observation tank (Nmale = Nfemale = 10).
A.
B.
...
Côté, I.M. & Verde, E.A., eds. Diving for Science 2019:
Proceedings of the American Academy of Underwater Sciences 38th Symposium.
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Figure 13. Full-body chromatic signals commonly used by initiators (A) and reactors (B) of an
interaction. Octopus rubescens were allowed to interact with conspecifics in Male/Male,
Male/Female, and Female/Female pairs in an observation tank (Nmale = Nfemale = 10).
A.
B.
Côté, I.M. & Verde, E.A., eds. Diving for Science 2019:
Proceedings of the American Academy of Underwater Sciences 38th Symposium.
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Figure 14. Postural signals commonly used by initiators (A) and reactors (B) of an interaction. Octopus
rubescens were allowed to interact with conspecifics in Male/Male, Male/Female, and
Female/Female pairs in an observation tank (Nmale = Nfemale = 10).
A.
B.
Côté, I.M. & Verde, E.A., eds. Diving for Science 2019:
Proceedings of the American Academy of Underwater Sciences 38th Symposium.
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Visual signals are especially important for octopuses to use during aggressive interactions because they
can clearly display an octopus’s intentions to attack or submit, depending on the likelihood of winning
or losing a fight (Barbato et al., 2007; Scheel et al., 2016). Having the ability to display such intent
helps octopuses avoid unnecessary harm. Octopus rubescens used specific and discrete visual signs (the
‘attack’ posture and chromatic signals ‘deimatic’ and ‘dark longitudinal stripes’) to warn a conspecific
before attacking. The ‘attack’ posture, although not used as frequently as other postures, such as
‘upright’ and ‘curled arms’, is an important example of a warning system that this species used before
attacking a conspecific. The chromatic signal ‘deimatic’ was also used to warn or threaten a conspecific
and is a commonly used threatening display posture among other cephalopods (Scheel et al., 2016;
Hanlon and Messenger, 2018). Furthermore, O. rubescens displayed ‘dark longitudinal stripes’, similar
to Abdopus aculeatus (Huffard, 2007), prior to or while reaching for a conspecific or before attacking.
Another noteworthy chromatic signal O. rubescens used was ‘false frontal white eye spots’ which
appeared quite frequently and was interpreted as another warning sign toward conspecifics. This signal,
along with ‘dark longitudinal stripes’, was included in Hanlon and Messenger’s (2018) descriptive table
of visual signals commonly used by cephalopods. Both forms of communication are examples of how
octopuses produce high-contrasting chromatic patterns that are easily visible to an observer. Lastly, O.
rubescens displayed the posture ‘stand tall’, similar to Octopus tetricus and Abdopus aculeatus
(Huffard, 2007; Scheel et al., 2016). While O. rubescens did not use this posture as frequently as
‘upright’ or ‘curled arms’, it is an important posture that should enable individuals to get a better view
of a conspecific or to increase apparent size of an individual (Huffard, 2007; Scheel et al., 2016).
One aggressive signal, ‘grappling’, was not as frequent as other postural or locomotor signals, but
nonetheless occurred during interactions and most frequently between males. Huffard (2007) observed
similar agonistic interactions primarily between males compared to M/F interactions; no F/F
interactions were observed by Huffard (2007) to serve as a comparison with the behaviors documented
for O. rubescens. Increased aggression between males perhaps could be attributed to their need to
compete for females in their natural habitat. Huffard et al. (2010) suggest that M/M aggression is
influenced by the value of a resource being competed for (a female) and the likelihood that a male can
successfully acquire that resource. Therefore, an aggressive interaction between males may determine
whether a male copulates with a preferred female or not which may explain why males are more likely
to be aggressive toward one another.
Since the sample of octopuses used in this study was from a population in Admiralty Bay, where they
congregate to use bottles as dens, these octopuses may use a specialized system of visual signaling
during interactions to communicate with conspecifics, as opposed to more solitary octopuses. Caldwell
et al. (2015) suggest octopus populations with higher local densities interact with conspecifics more
frequently and often display more aggression toward conspecifics compared to solitary octopus species.
Consequently, the observed agonistic interactions of O. rubescens may be due to the denser population
of this species in Admiralty Bay. As a result, this population of octopuses may experience increased
competition for dens (due to increased encounter rates), mates or food which may lead to increased
aggression (Huffard et al., 2010).
Although the behaviors documented were in a laboratory setting, the ethogram produced in this study
may still serve as a useful reference. Future studies can document the visual signals of O. rubescens
collected from other habitats and reveal potential variations in visual signals used by this species. This
may allow scientists to hypothesize that the visual signals used by O. rubescens are influenced by
surrounding habitats, like Admiralty Bay, or population density. The basic ethogram created in this
study can also act as an additional resource of comparison between octopus species, regardless of the
fact that the visual cues identified were during conspecific interactions. Ethograms can be helpful
resources that demonstrate evolutionary convergence of signal use (e.g. two distantly related species
using similar signals to communicate with conspecifics) or verify a taxonomic similarity between
species (Huffard, 2007).
Côté, I.M. & Verde, E.A., eds. Diving for Science 2019:
Proceedings of the American Academy of Underwater Sciences 38th Symposium.
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Acknowledgements
This research was supported by the Women Divers Hall of Fame, Quahog Bay Conservancy, and Maine
Maritime Academy; all deserve great thanks for their interest in this study and the financial aid provided.
We are grateful for the team at RBML; a special thank you to Jim Nestler and Joe Galusha who provided
diving logistics and behavior analysis, respectively, and to Monica Culler, and Katie Pekar for being
willing to dive to help collect and release octopuses. We are thankful for the support of the MMA Ocean
Studies department, especially Ann Cleveland who provided her insight and expertise in animal
behavior and statistics.
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Appendix
Settings used on the GoPro cameras to capture clear videos of octopuses in high-light situations (GoPro
Hero 3 Black Edition User Manual; GoPro Hero 3+ Silver Edition User Manual). Cameras were placed
at different locations in an observation tank to record visual signals displayed by octopuses during
conspecific interactions.
GoPro Hero 3
GoPro Hero 3+
Pixels
1080
1440
Frames per Second
30
30
Protune
On
On
White Balance
Auto
Auto
Field of View
Wide
Wide
GoPro Hero 3 Black Edition User Manual [Internet]. 2018. San Mateo (CA): GoPro; [cited 2018 Feb
19]. https://gopro.com/content/dam/help/hero3-black-edition/manuals/HERO3
GoPro Hero 3+ Silver Edition User Manual [Internet]. 2018. San Mateo (CA): GoPro; [cited 2018 April
10]. https://cbcdn2.gp-static.com/uploads/product_manual/file
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